Urine Output Calculator — mL/kg/hr & AKI Staging

Calculate urine output rate (mL/kg/hr), classify oliguria/anuria/polyuria, and assess KDIGO AKI staging by urine output. Supports adults, children, infants, and neonates with hourly tracking.

⚠️ Clinical Tool: Urine output monitoring is a key component of fluid management and AKI assessment. Trends over time matter more than single measurements. Always correlate with serum creatinine, clinical status, and fluid balance.

Patient & Measurement

Hourly Tracker (optional — enter mL per hour)

Hourly Rate
50 mL/h
0.71 mL/kg/hr
Daily Projected
1200 mL/day
17.1 mL/kg/day
Status
Normal urine output
Normal: 0.5–1.5 mL/kg/hr (800–2000 mL/day)
KDIGO AKI (by UO)
Not meeting AKI UO criteria
Requires concurrent creatinine assessment
0.71 mL/kg/hr — Normal urine output

Normal range: 0.5–1.5 mL/kg/hr (800–2000 mL/day)

KDIGO AKI Classification (Urine Output Criteria)

AKI StageUrine Output CriteriaCreatinine Criteria
Stage 1< 0.5 mL/kg/h for 6–12 h↑ 1.5–1.9× baseline or ↑ ≥ 0.3 mg/dL
Stage 2< 0.5 mL/kg/h for ≥ 12 h↑ 2.0–2.9× baseline
Stage 3< 0.3 mL/kg/h for ≥ 24 h or anuria ≥ 12 h↑ 3.0× baseline or ≥ 4.0 mg/dL or RRT initiated

Urine Output Differential

CategoryDefinitionCommon Causes
Anuria< 100 mL/dayObstructive uropathy, bilateral renal artery occlusion, cortical necrosis
Oliguria< 0.5 mL/kg/hrPrerenal (dehydration, heart failure), intrinsic renal injury, obstruction
Normal0.5–1.5 mL/kg/hrAdequate hydration and renal function
Polyuria> 3 L/dayDiabetes insipidus, osmotic diuresis, psychogenic polydipsia, post-obstructive
Planning notes, formulas, and examples

About the Urine Output Calculator — mL/kg/hr & AKI Staging

Urine output is one of the most fundamental and readily available markers of organ perfusion and renal function. Quantifying output in mL/kg/hr standardizes measurement across body sizes and is essential for recognizing acute kidney injury (AKI), guiding fluid resuscitation, and monitoring critically ill patients. The KDIGO guidelines use urine output as one of two criteria (alongside creatinine) for AKI staging.

Normal adult urine output ranges from 0.5 to 1.5 mL/kg/hr (approximately 800–2,000 mL/day). Oliguria (< 0.5 mL/kg/hr) signals inadequate renal perfusion or intrinsic renal injury, while anuria (< 100 mL/day or < 0.1 mL/kg/hr) suggests complete obstruction or severe bilateral renal injury. Polyuria (> 3 L/day) may indicate diabetes insipidus, osmotic diuresis, or post-obstructive diuresis. Age-specific thresholds differ: neonates and infants normally produce 1–3 mL/kg/hr.

This calculator converts total urine volume over any time period to standardized mL/kg/hr and mL/kg/day, applies age-appropriate classification (adult, child, infant, neonate), maps output to KDIGO AKI staging, and includes an optional hourly tracker with visual trend bars for bedside monitoring. It is a tracking worksheet, not a substitute for broader renal assessment.

When This Page Helps

Urine output is arguably the single most important bedside vital sign for assessing organ perfusion and renal function, yet manual calculation of mL/kg/hr is error-prone — especially during busy nursing shifts. An incorrect weight, wrong time interval, or arithmetic error can lead to missed oliguria or unnecessary interventions. It shows instant, accurate conversion with age-appropriate classification and AKI staging.

How to Use the Inputs

  1. Select the patient population (adult, child, infant, or neonate).
  2. Enter body weight in kilograms.
  3. Enter total urine output in mL and the collection period in hours.
  4. Optionally enter individual hourly measurements for trend tracking.
  5. Review the calculated rate (mL/kg/hr), classification, and KDIGO AKI stage.
  6. Monitor trends using the visual hourly bar chart.
Formula used
Hourly rate (mL/h) = Total output (mL) / Hours mL/kg/hr = Hourly rate / Body weight (kg) Daily projected = Hourly rate × 24 KDIGO AKI: Stage 1 = < 0.5 mL/kg/hr × 6h; Stage 2 = < 0.5 × 12h; Stage 3 = < 0.3 × 24h or anuria × 12h

Example Calculation

Result: 0.31 mL/kg/hr — Oliguria (KDIGO AKI Stage 1)

200 mL ÷ 8 hours = 25 mL/hr. 25 ÷ 80 kg = 0.31 mL/kg/hr. This is below the oliguria threshold of 0.5 mL/kg/hr. Over 8 hours (> 6h threshold), this meets KDIGO AKI Stage 1 urine output criteria.

Tips & Best Practices

  • Document urine output at consistent intervals (hourly in ICU, every 4-8 hours on the floor) for meaningful trend analysis.
  • A single hour of low output is not oliguria — KDIGO requires sustained low output over 6+ hours for AKI staging.
  • Always reconcile urine output with total fluid balance (ins vs outs) — positive balance with oliguria is different from negative balance with oliguria.
  • In post-operative patients, 6 hours of oliguria after major surgery is common and often resolves with hydration — but don't assume it's benign.
  • Polyuria after relief of urinary obstruction (post-obstructive diuresis) can be massive (>200 mL/hr) and requires careful fluid replacement.

When To Use This Calculator

Calculate urine output rate (mL/kg/hr), classify oliguria/anuria/polyuria, and assess KDIGO AKI staging by urine output. Supports adults, children, infants, and neonates with hourly tracking. Use it when you need a repeatable calculation in the health / general-health category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.

How To Check The Result

Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.

Practical Notes

Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.

Sources & Methodology

Last updated:

Methodology

This worksheet converts total urine volume and collection time into an hourly weight-adjusted output, then compares the result with age-specific thresholds and KDIGO urine-output staging. It is intended for bedside trend review, not as a standalone diagnosis of kidney injury.

The page keeps neonatal, infant, and adult ranges distinct because normal urine output differs substantially across age groups.

Sources

  • KDIGO Clinical Practice Guideline for Acute Kidney Injury (Kidney Disease: Improving Global Outcomes) — Urine-output criteria for AKI staging.
  • Urine output monitoring and AKI reviews (Nephrology review literature) — Context for mL/kg/hr thresholds and clinical interpretation.
  • Pediatric and neonatal renal physiology references (Nephrology / pediatrics textbooks) — Age-specific urine output norms.

Frequently Asked Questions

  • No. KDIGO requires either urine output criteria OR creatinine criteria to diagnose AKI. Urine output can be misleading in certain situations (e.g., diuretic use, osmotic diuresis). Always correlate with serum creatinine, fluid balance, and clinical context.

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